1. Field of the Invention
The present invention relates to a method for adjusting a recording substrate and at least one array relative to each other, the recording substrate and the at least one array having a relative position with respect to each other, the at least one array being part of a printing device having a carrying structure for mounting said array and having nozzles arranged in a row substantially parallel to a first direction for forming second test marks on the recording substrate, wherein the recording substrate comprises a pre-printed pattern containing first test marks, the method comprising forming a test pattern containing the first and second test marks, each first and second test mark having a location on the substrate, and detecting the locations of the first and second marks.
2. Description of Background Art
In an ink jet printer known from the background art and having at least one printhead, a carriage whereon the printhead is mounted is generally moved over a recording substrate in a main scanning direction parallel to a y-axis for the purpose of recording a swath of an image. The printhead has at least one array of nozzles extending in a direction substantially parallel to the x-axis, which is the sub-scanning direction. The sub-scanning direction x is perpendicular to the main scanning direction y. An image swath consisting of a certain number of pixel lines, corresponding to the number of activated nozzles of the printhead is thus recorded during a pass of the carriage along the main scan direction. In a given relative position of the array and the substrate along the x-axis, the array and the recording substrate at least partially flank each other and are arranged for applying second test marks (also referred to as dots) on a substrate, which is pre-printed by first test marks. Some pixel lines are thus constituted by the second test marks, corresponding to the nozzles of the array, while other pixel lines are constituted by first test marks which are pre-printed on the recording substrate. The first test marks form a pre-printed pattern already present on the recording substrate before printing the second test marks. The pre-printed pattern may be printed on the substrate with the same printing device or another printing device. The pre-printed pixel lines are thus constituted on the recording substrate by the first test marks, which together with the printed second test marks form a test pattern. Generally, interlacing of the pixel lines constituted by the first test marks and pixel lines constituted by the second test marks is desired to obtain a high resolution of the recording image and the spacing between the lines should be as regular as possible. During one single pass of the carriage over a pre-printed recording substrate, a printing resolution twice as high as the resolution of the single array may be achieved. Therefore, the locations of the first and second test marks should be compared and analyzed in order to determine the relative position of the array and the substrate along the x-axis. The determined relative position may have to be adjusted to reach a high degree of precision in the desired relative positioning of the substrate and the array. Deviations in the test pattern may be detected and may be used to adjust the relative position of the array and the substrate. Furthermore, a common error in the positioning of pixels is caused by jet angles which deviate from the ideal jet angle. Such defects may be caused by impurities present in the nozzles. Such defects may lead to deviations between the positioning of the first and second marks. Deviations in positioning of a first test mark may be caused during pre-printing of the first test marks on the substrate and deviations in positioning of a second test mark may be caused during printing of the second test marks by the array on the pre-printed substrate. Such defects may lead, for graphical applications, to the appearance of white or light stripes in an image, known as a “banding” effect. When inkjet technology is applied as a manufacturing technique for printed electronics, for example, the number of positioning errors must be extremely minimized towards zero.
From DE 19829280A1, a method is known for determining a relative position of a first and a second imaging device. The method includes setting an image of a reference pattern by the first imaging device on a recording substrate, setting an image of a reference pattern by the second imaging device on the same part of the recording substrate, resulting in a combination pattern. The relative position of the first and second image device can be determined from the combination pattern.
From U.S. Application Publication No. 2003/0144815, another method is known wherein the relative position of two patterns printed by a first and a second image device is determined by means of a basic pattern being already present on a recording substrate before the setting of the images by the first and second image device.